Water, methane, and ammonia are commonly considered to be the key components of the interiors of Uranus and Neptune. Modelling the planets’ internal structure, evolution, and dynamo heavily relies on the properties of the complex mixtures with uncertain exact composition in their deep interiors. Therefore, characterising icy mixtures with varying composition at planetary conditions of several hundred gigapascal and a few thousand Kelvin is crucial to improve our understanding of the ice giants. In this work, pure water, a water-ethanol mixture, and a water-ethanol-ammonia “synthetic planetary mixture” (SPM) have been compressed through laser-driven decaying shocks along their principal Hugoniot curves up to 270, 280, and 260 GPa, respectively. Measured temperatures spanned from 4000 to 25000 K, just above the coldest predicted adiabatic Uranus and Neptune profiles (3000–4000 K) but more similar to those predicted by more recent models including a thermal boundary layer (7000–14000 K). The experiments were performed at the GEKKO XII and LULI2000 laser facilities using standard optical diagnostics (Doppler velocimetry and optical pyrometry) to measure the thermodynamic state and the shock-front reflectivity at two different wavelengths. The results show that water and the mixtures undergo a similar compression path under single shock loading in agreement with Density Functional Theory Molecular Dynamics (DFT-MD) calculations using the Linear Mixing Approximation (LMA). On the contrary, their shock-front reflectivities behave differently by what concerns both the onset pressures and the saturation values, with possible impact on planetary dynamos.

水，甲烷和氨通常被认为是天王星和海王星内部的关键成分。对行星的内部结构，演化和发电机进行建模的过程在很大程度上取决于复杂混合物的属性，这些复杂混合物在其深部内部不确定确切的组成。因此，在数百吉帕斯卡和几千开尔文的行星条件下表征成分不同的冰冷混合物对于增进我们对冰巨星的了解至关重要。在这项工作中，纯水，水-乙醇混合物和水-乙醇-氨“合成行星混合物”（SPM）已通过沿其主要Hugoniot曲线（高达270、280和260）的激光驱动的衰减冲击而被压缩。 GPa分别。测得的温度范围为4000至25000 K，刚好高于最冷的绝热天王星和海王星剖面（3000–4000 K），但与包括热边界层（7000–14000 K）的最新模型所预测的更为相似。实验是在GEKKO XII和LULI2000激光设备上使用标准的光学诊断程序（多普勒测速仪和光学高温计）进行的，以测量两种不同波长下的热力学状态和激波前反射率。结果表明，与使用线性混合近似（LMA）的密度泛函理论分子动力学（DFT-MD）计算相一致，水和混合物在单次冲击载荷下会经历相似的压缩路径。相反，它们的冲击前反射率在开始压力和饱和度值两方面都表现出不同的表现，